Patent Application
20220144416
The present disclosure relates in general to vibration control. More specifically, the present disclosure relates to a novel design of an apparatus for isolating mechanical vibrations in structures or bodies that are subject to harmonic or oscillating displacements or forces over a wide range of frequencies. The apparatus of the present disclosure is well suited for use in the field of aircraft, in particular, helicopters and other rotary wing aircraft.
For many years, effort has been directed toward the design of an apparatus for isolating a vibrating body from transmitting its vibrations to another body. Such apparatuses are useful in a variety of technical fields in which it is desirable to isolate the vibration of an oscillating or vibrating device, such as an engine, from the remainder of the structure. Typical vibration isolation and attenuation devices (“isolators”) employ various combinations of the mechanical system elements (springs and mass) to adjust the frequency response characteristics of the overall system to achieve acceptable levels of vibration in the structures of interest in the system. One field in which these isolators find a great deal of use is in aircraft, wherein vibration-isolation systems are utilized to isolate the fuselage or other portions of an aircraft from mechanical vibrations, such as harmonic vibrations, which are associated with the propulsion system, and which arise from the engine, transmission, and propellers or rotors of the aircraft.
Vibration isolators are distinguishable from damping devices in the prior art that are erroneously referred to as “isolators.” A simple force equation for vibration is set forth as follows:
F=m{umlaut over (x)}+c{dot over (x)}+kx
A vibration isolator utilizes inertial forces (m{umlaut over (x)}) to cancel elastic forces (kx). On the other hand, a damping device is concerned with utilizing dissipative effects (c{dot over (x)}) to remove energy from a vibrating system.
One important engineering objective during the design of an aircraft vibration-isolation system is to minimize the length, weight, and overall size including cross-section of the isolation device. This is a primary objective of all engineering efforts relating to aircraft. It is especially important in the design and manufacture of helicopters and other rotary wing aircraft, such as tilt rotor aircraft, which are required to hover against the dead weight of the aircraft, and which are, thus, somewhat constrained in their payload in comparison with fixed-wing aircraft.
Another important engineering objective during the design of vibration-isolation systems is the conservation of the engineering resources that have been expended in the design of other aspects of the aircraft or in the vibration-isolation system. In other words, it is an important industry objective to make incremental improvements in the performance of vibration isolation systems which do not require radical re-engineering or complete redesign of all the components which are present in the existing vibration-isolation systems.
A marked departure in the field of vibration isolation, particularly as applied to aircraft and helicopters is disclosed in U.S. Pat. No. 4,236,607, titled “Vibration Suppression System,” issued on Dec. 2, 1980, to Halwes, et al. (“Halwes '607”). Halwes '607 is incorporated herein by reference. Halwes '607 discloses a vibration isolator, in which a dense, low-viscosity fluid is used as the “tuning” mass to counterbalance, or cancel, oscillating forces transmitted through the isolator. This isolator employs the principle that the acceleration of an oscillating mass is 180° out of phase with its displacement.
In Halwes '607, it was recognized that the inertial characteristics of a dense, low-viscosity fluid, combined with a hydraulic advantage resulting from a piston arrangement, could harness the out-of-phase acceleration to generate counter-balancing forces to attenuate or cancel vibration. Halwes '607 provided a much more compact, reliable, and efficient isolator than was provided in the prior art. The original dense, low-viscosity fluid contemplated by Halwes '607 was mercury, which is toxic and highly corrosive.
Since Halwes' early invention, much of the effort in this area has been directed toward replacing mercury as a fluid or to varying the dynamic response of a single isolator to attenuate differing vibration modes. An example of the latter is found in U.S. Pat. No. 5,439,082, titled “Hydraulic Inertial Vibration Isolator,” issued on Aug. 8, 1995, to McKeown, et al. (“McKeown '082”). McKeown '082 is incorporated herein by reference. An example of the former is found in U.S. Pat. No. 6,022,600, titled “High-Temperature Fluid Mounting”, issued on Feb. 8, 2000, to Schmidt et al. (“Schmidt '600”). Schmidt '600 is incorporated herein by reference.
Several factors affect the performance and characteristics of the Halwes-type isolator, including the density and viscosity of the fluid employed, the relative dimensions of components of the isolator, and the like. One improvement in the design of such isolators is disclosed in U.S. Pat. No. 6,009,983, titled “Method and Apparatus for Improved Vibration Isolation,” issued on Jan. 4, 2000, to Stamps et al. (“Stamps '983”). In Stamps '983, a compound radius at each end of the tuning port was employed to provide a marked improvement in the performance of the isolator. Stamps '983 is incorporated herein by reference.
Another area of improvement in the design of the Halwes-type isolator has been in an effort directed toward a means for changing the isolator's frequency in order to increase the isolator's effectiveness during operation. One development in the design of such isolators is disclosed in U.S. Pat. No. 5,435,531, titled “Vibration Isolation System,” issued on Jul. 25, 1995, to Smith et al. (“Smith '531”). Smith '531 is incorporated herein by reference. In Smith '531, an axially extendable sleeve is used in the inner wall of the tuning port in order to change the length of the tuning port, thereby changing the isolation frequency. Another development in the design of tunable Halwes-type isolators was disclosed in U.S. Pat. No. 5,704,596, titled “Vibration Isolation System,” issued on Jan. 6, 1998, to Smith et al. (“Smith '596”). Smith '596 is incorporated herein by reference. In Smith '596, a sleeve is used in the inner wall of the tuning port in order to change the cross-sectional area of the tuning port itself, thereby changing the isolation frequency during operation. Both Smith '531 and Smith '596 were notable attempts to actively tune the isolator.
Another development in the area of vibration isolation is the tunable vibration isolator disclosed in U.S. Pat. No. 6,695,106, titled “Method and Apparatus for Improved Vibration Isolation,” issued on Feb. 24, 2004, to Smith et al (“Smith '106”). Smith '106 is incorporated herein by reference.
An additional development in the area of vibration isolation is the external tuning port disclosed in U.S. patent application Ser. No. 15/240,797, titled “Liquid Inertia Vibration Elimination System,” filed on Aug. 18, 2016, which is incorporated herein by reference. Although the foregoing developments represent great strides in the area of vibration isolation, a need for systems capable of reducing vibrations of significantly higher frequencies than the above-described vibration reduction systems remains.
Prior Art
In this disclosure, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of this disclosure, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower,” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction. In addition, the use of the term “coupled” throughout this disclosure may mean directly or indirectly connected, moreover, “coupled” may also mean permanently or removably connected, unless otherwise stated.
This disclosure provides a liquid inertia vibration elimination (“LIVE”) system having a compound periodic strut configured to reduce vibrations of much greater frequency as compared to a tuned frequency of a traditional LIVE system. The compound period strut is made possible by the systems and methods disclosed in (1) Chinese Patent No. 104408488, titled “Compound Helicopter Main Reducing Period Support Rod,” issued on Dec. 8, 2017 to UNIV NANJING AERONAUTICS & ASTRONAUTICS (Chinese Patent '488), (2) Wang, F., Lu, Y. and Li, J., “Helicopter Cabin Noise Reduction Based on Compound Period Struts,” American Helicopter Society 74th Annual Forum Proceedings, Phoenix, Ariz., USA, May 14-17, 2018 (AHS Wang/Lu/Li), and (3) Lu, Y., Wang, F., and Ma, X., “Research on the Vibration Characteristics of a Compounded Periodic Strut Used for Helicopter Cabin Noise Reduction,” Shock and Vibration, Vol. 2017, Article ID 4895026, http://doi.org/10.1155/2017/4894026 (Shock and Vibration Lu/Wang/Ma). Chinese Patent '488, AHS Wang/Lu/Li, and Shock and Vibration Lu/Wang/Ma are each incorporated herein by reference.
Referring now to
Referring to
Struts 214 are attached to central bearing housing 210 using fasteners 220, which in this embodiment comprise bolts. Struts 214 are further attached to trusses of internal frame 120 using spherical truss attachment bearings 222 and pins 224. Struts 214 can transfer thrust and torque loads to internal frame 120. Spherical truss attachment bearings 222 allow for moment alleviation and dynamic tuning.
During operation of LIVE systems 200, the introduction of a force into piston 208 translates piston 208 relative to upper end cap 228 and lower end cap 230. Such a displacement of piston 208 forces tuning fluid that is disposed within the fluid flow path to move through central port 226 in the opposite direction of the displacement of piston 208. Such a movement of tuning fluid produces an inertial force that cancels, or isolates, the force from piston 208. During typical operation, the force imparted on piston 208 is oscillatory; therefore, the inertial force of the tuning fluid is also oscillatory, the oscillation being at a discrete frequency, i.e., isolation frequency.
Referring now to Prior Art
Referring now to
Referring to
While the LIVE systems disclosed herein comprise a passive system for combating vibration at frequencies lower than 2*n/rev, in alternative embodiments, actively controlled LIVE systems may be utilized that perform an electronically controlled actuation and/or an electronically controlled tuning of the isolation frequency. Further, the frequency response of the struts can be tuned during design by changing materials, geometries, and/or sizes of the internal components of the struts as well as, in some cases, electronically controlling a material property, geometry, and/or size of one or more internal components of the struts. Further, it will be appreciated that the struts 214, 304 disclosed herein are shown schematically to demonstrate one embodiment of an interior construction.
At least one embodiment is disclosed, and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, Rl, and an upper limit, Ru, is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=Rl+k*(Ru−Rl), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 95 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present invention. Also, the phrases “at least one of A, B, and C” and “A and/or B and/or C” should each be interpreted to include only A, only B, only C, or any combination of A, B, and C.
